Nonlinear contributions to the quasistatic and the first-harmonic dielectric response in relaxor systems

Nonlinear dielectric response in relaxor systems was studied as a function of the ac and dc electric field. Significant frequency dependence was found in the nonlinearity a(3). The crossover temperature dependence of a(3) -a fingerprint of the spherical glass freezing- was confirmed to exist even in the static limit. Beside the expected reflection of the third harmonic component epsilon (3)(3 omega) additional nonlinear contribution was found in the nonlinear dependence of the first harmonic response epsilon (1)(omega). It is shown that this second contribution to the field dependence of epsilon (1)(omega) and also the quasistatic measurements of the nonlinear dielectric response throughout the glassy-to-ferroelectric crossover region can be described by the spherical random-bond-random-field model of relaxor ferroelectrics.